It is narrated from Nafi' that Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) would not do more than the iqamah for the prayer while travelling (that is, he would not give the adhan), except for the morning prayer, for which he would give the adhan and the iqamah, and he would say: The adhan is for the imam with whom the people gather.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 1944